This application claims priority from Japanese Patent Application No. 2002-081937 filed Mar. 22, 2002, which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an ink-jet printing apparatus and an ink-jet printing method, more particularly, to control of driving a liquid ejection head having electro-thermal converting elements to generate thermal energy used for ejecting ink.
2. Description of the Related Art
One of the generally known ink jet printing apparatuses is that which causes a printing head, for ejecting the ink, to scan in a main scanning direction and causes the printing head to eject ink from nozzles thereof according to driving signals generated from the image data signal, so as to form an image on a printing medium.
Further, printing heads used in this kind of ink jet printing apparatus are generally those described below in terms of ink ejecting methods.
More specifically, the ink ejecting method includes a method using, as an ejection energy generating element for applying energy to eject ink, an electro-thermal converting element (a heater) for generating a bubble to eject the ink, and a method using, as the ejection energy generating element, the piezoelectric element deforming to eject ink. Both these methods enable the ink to be ejected by inputting an electrical signal to the ejecting energy generating element; the former method has an advantage in that a space required for arranging a heater, as being the ejecting energy generating element, is relatively small, and such advantage also contributes not only to simplifying the construction of and reducing the size of the printing head but also to relatively easy accomplishment of the high resolution of ejection orifices.
On the other hand, this method is apt to cause the heat from the heater to be accumulated in the printing head, resulting in a change in the volume of the ink drops to be ejected. Further, cavitation resulting from the break of the bubble sometimes has a serious effect on the performance of the heater.
As the known methods for resolving such problems there are those ink-jet printing methods and the ink-jet printing heads described in, for example, Japanese Patent Application Laying-open No.54-161935 (1979), Japanese Patent Application Laying-open No.61-185455 (1986), Japanese Patent Application Laying-open No. 61-249768 (1986) and Japanese Patent Application Laying-open No. 4-10941 (1992). Each of the printing heads described in these publications has a structure including an ejection orifice for ejecting the liquid, an ink passage communicating with the ejection orifice and filled with the ink and an electro-thermal converting element provided in the ink passage. The electro-thermal converting element, in general, comprises a thin-film resistor, to which a pulse from an electric current (drive pulse) is applied through an electric wire to generate the heat energy. Then, the heat energy causes the air bubble to be generated in the ink to eject the ink, such that the ink is ejected while keeping the air bubble communicating with outside air. Employing this ink ejection method enables stabilization of the volume of ejected ink drops to be improved, high-speed printing with small ink drops and lengthening of the service life of the heater by eliminating occurrence of cavitation caused by the break of the bubble.
However, in the conventional printing head described above, it sometimes occurs that the temperature of the printing head rises especially when ink ejection is continuously performed with high ejection duty (corresponding to a rate of ejected inks to pixels of a predetermined area; in the case of ejecting one ink to each pixel in the predetermined area, the duty is 100%). Such rise of the temperature causes the size of the air bubble to become larger than normal size, thereby causing the amount of moved ink or the moving distance of ink to increase in the ink passage, so that ink is not effectively refilled to the ink passage. As a result, a frequency response characteristic of the printing head decreases.
Taking account of the decrease of the frequency response characteristic to the drive pulse due to the rise of the temperature of the printing head, it can be considered to set the drive frequency to a uniformly lower level. However, this results in overall decrease of a throughput.
On the other hand, for example, Japanese Patent No. 2543952 discloses a method in which the temperature of the printing head is detected and the drive frequency is controlled depending on the detected temperature. However, in the case of the art disclosed in the Japanese Patent, the drive speed of the printing head is lowered immediately after the temperature of the printing head has exceeded a predetermined level of the temperature, so that the decrease tendency of the overall throughput remains unchanged. In order to prevent the throughput from decreasing, there is available a method wherein when the rise of the temperature occurs, the energy to be input to the heater is reduced to suppress the growth of the bubbles. This method, however, gives rise to a problem that when the ink ejection is performed continuously with high ejection duty while the input of the energy is reduced, the drive pulse voltage decreases to decrease an ejection amount of the ink, thereby causing a blur of the printed image in the worst case.
The object of the present invention is to provide an ink-jet printing method and an ink-jet printing apparatus which is capable of avoiding degradation of a printed image accompanied by a decrease of a refilling characteristic caused by a rise of the temperature of a printing head and preventing a printing speed from decreasing.
In the first aspect of the present invention, there is provided an ink jet printing method using an ink ejecting head having a plurality of ejection orifices and an electro-thermal converting element for generating thermal energy for ejecting ink from the plurality of ejection orifices to perform printing on a printing medium, the method comprising:
a setting step for obtaining temperature of the ink ejecting head and changing settings of a pulse width and a drive voltage of a drive pulse to be applied to the electro-thermal converting element; and
a control step for controlling driving of the electro-thermal converting element with the drive pulse having the pulse width and the drive voltage based on a result set by the setting step,
wherein the setting step relatively shortens the pulse width and relatively raises the drive voltage as the temperature of the ink ejecting head relatively rises.
In the second aspect of the present invention, there is provided an ink jet printing apparatus using an ink ejecting head having a plurality of ejection orifices and an electro-thermal converting element for generating thermal energy for ejecting ink from the plurality of ejection orifices to perform printing on a printing medium, the apparatus comprising:
setting means for obtaining temperature of the ink ejecting head and changing settings of a pulse width and a drive voltage of a drive pulse to be applied to the electro-thermal converting element; and
control means for controlling driving of the electro-thermal converting element with the drive pulse having the pulse width and the drive voltage based on a result set by the setting means,
wherein the setting means relatively shortens the pulse width and relatively raises the drive voltage as the temperature of the ink ejecting head relatively rises.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.